CO_2对离体欧芹叶片中蛋白质代谢的影响

以离体欧芹叶片为实验系统 ,研究了CO2 对叶片中蛋白质降解的影响。对离体欧芹叶片中游离氨基酸含量及可溶蛋白含量的分析结果表明 :CO2 具有抑制离体欧芹叶片中蛋白质降解的作用 ,这为进一步了解CO2 延缓叶片衰老的作用机理很有意义。     

The safety of adult male circumcision in HIV-infected and uninfected men in Rakai, Uganda

Background

The objective of the study was to compare rates of adverse events (AEs) related to male circumcision (MC) in HIV-positive and HIV-negative men in order to provide guidance for MC programs that may provide services to HIV-infected and uninfected men.

Methods and Findings

A total of 2,326 HIV-negative and 420 HIV-positive men (World Health Organization [WHO] stage I or II and CD4 counts > 350 cells/mm³) were circumcised in two separate but procedurally identical trials of MC for HIV and/or sexually transmitted infection prevention in rural Rakai, Uganda. Participants were followed at 1–2 d and 5–9 d, and at 4–6 wk, to assess surgery-related AEs, wound healing, and resumption of intercourse. AE risks and wound healing were compared in HIV-positive and HIV-negative men. Adjusted odds ratios (AdjORs) were estimated by multiple logistic regression, adjusting for baseline characteristics and postoperative resumption of sex. At enrollment, HIV-positive men were older, more likely to be married, reported more sexual partners, less condom use, and higher rates of sexually transmitted disease symptoms than HIV-negative men. Risks of moderate or severe AEs were 3.1/100 and 3.5/100 in HIV-positive and HIV-negative participants, respectively (AdjOR 0.91, 95% confidence interval [CI] 0.47–1.74). Infections were the most common AEs (2.6/100 in HIV-positive versus 3.0/100 in HIV-negative men). Risks of other complications were similar in the two groups. The proportion with completed healing by 6 wk postsurgery was 92.7% in HIV-positive men and 95.8% in HIV-negative men (p = 0.007). AEs were more common in men who resumed intercourse before wound healing compared to those who waited (AdjOR 1.56, 95% CI 1.05–2.33).

Conclusions

Overall, the safety of MC was comparable in asymptomatic HIV-positive and HIV-negative men, although healing was somewhat slower among the HIV infected. All men should be strongly counseled to refrain from intercourse until full wound healing is achieved.Trial registration: http://www.ClinicalTrials.gov; for HIV-negative men, #{"type":"clinical-trial","attrs":{"text":"NCT00047073","term_id":"NCT00047073"}}NCT00047073 and for HIV-positive men, #{"type":"clinical-trial","attrs":{"text":"NCT00047073","term_id":"NCT00047073"}}NCT00047073.     

CO2对离体欧芹叶片中蛋白质代谢的影响

以离体欧芹叶片为实验系统,研究了CO2对叶片中蛋白质降解的影响。对离体欧芹叶片中游离氨基酸含量及可溶蛋白含量的分析结果表明:CO2具有抑制离体欧芹叶片中蛋白质降解的作用,这为进一步了解CO2延缓叶片衰老的作用机理很有意义。     

Role of ethylene in senescence of watercress leaves

Detached watercress leaves showed a rapid senescence rate as compared with other herbs. It was therefore of interest to investigate the role of ethylene in the rapid senescence of watercress leaves, and So estimate the efficacy of various inhibitors of elhylene synthesis (aminoethoxyvinylglycine, AVG) and action (CO₂, Ag⁺) in retarding senescence processes. The progress of senescence in watercress bunches (leaves attached to cut stems) and in detached leaves was estimated by measuring the rate of chlorophyll (Chl) loss, proteolysis and lipid oxidation. Evidence is presented showing that application of 11% CO₂ to watercress bunches in a flow-through system had a long-lasting effect on senescence, exhibited by highly efficient retardation of all the senescence processes tested. On the other hand, application of AVG (O.1 m M ) or Ag-(30 μ M ) to detached leaves affected Chl loss much more than prciteolysis. These results suggest that the senescence-retarding activity of CO₂ cannot be attributed solely to its action as an anli-ethylene agent and that not all senescence-associated processes are regulated by ethylene.     

Interrelationship between ethylene and growth regulators in the senescence of lettuce leaf discs

The interrelationship between ethylene and growth regulators in the senescence of romaine lettuce (Lactuca sativa L.) leaves was studied. Gibberellic acid (GA₃), kinetin, and 3-indoleacetic acid (IAA) retarded chlorophyll loss from leaf discs which were floated on hormone solutions. Abscisic acid (ABA) and ethephon enhanced chlorophyll loss and antagonized the senescence-retarding effect of GA₃ and kinetin. A high concentration of IAA (10^–4 M) caused accelerated chlorophyll loss, whereas a similar concentration of kinetin neither retarded nor promoted chlorophyll loss. The ineffectiveness of IAA and kinetin at their supraoptimal concentrations in retarding leaf senescence was related to increased production of ethylene induced in the treated leaf discs. GA₃ was the most effective in retarding chlorophyll loss and did not stimulate ethylene production at all. The senescence-enhancing effect of ABA was not mediated by ethylene. However, the moderately increased production of ethylene, induced by relatively high concentrations of ABA, could act synergistically with the latter to accelerate chlorophyll loss. It is proposed that the effectiveness of exogenously applied hormones, both in enhancing and retarding senescence, is greatly affected by the endogenous ethylene concentration of the treated plant tissue.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 2571-E, 1988 series.     

In situ nitrogen fixation associated with seagrasses in the Gulf of Elat (Red Sea)

In situ nitrogen fixation associated with the seagrass Halophila stipulacea, at the northern Gulf of Elat (Red Sea), is eight to ten times higher than that of nearby plant-free areas. A daily cycle of nitrogen fixation is evident, with rates during the day being seven times greater than during the night. Removal of seagrass leaves only from a patch within a seagrass bed gradually decreases nitrogen fixation activity, reaching the rates of plant-free areas after ten hours. A method devised for the in situ measurement of nitrogen fixation rates using belljars is described in detail. Nitrogen fixation rates in situ are higher than in the laboratory and lack the lag period typical to laboratory measurements. In laboratory experiments using intact plant samples, glucose enhances nitrogen fixation rates both in light and dark. Photosystem II inhibitor (3-3,4-dichloro-phenyl-1,1-dimethylurea) doubles nitrogen fixation rates in light. Both field and laboratory results indicate that light is essential for nitrogen fixation activity in the H. stipulacea bed possibly through its effect on cyanobacterial population that occupy the aerobic niches of the phyllosphere and on photosynthetic Rhodospirillacean bacteria that inhabit the anaerobic ones. Nitrogen fixation rates evident in H. stipulacea beds in situ account for a considerable portion of the biomass production by the seagrasses. The dependence of high nitrogenase activity by the diazotrophs on the presence of the seagrasses indicates the great importance of the seagrass community to the nitrogen cycle in its highly oligotrophic surroundings of the Gulf of Elat.     

Quantitative relationships between osmotic potential amd epicotyl growth in Vigna radiata as affected by osmotic stress and cotyledon excision

Ethylene biosynthesis in leaf discs of tobacco ( Nicotiana tabacum L. cv. Xanthi), as measured by the conversion of L-[3,4-¹⁴C]-methionine to ¹⁴C₂H₄, was markedly inhibited by exogenous ethylene. This inhibition was accompanied by a decrease in total (free + conjugated) content of 1-aminocyclopropane-1-carboxylic acid (ACC), most of which appeared in its conjugated inactive form. The autoinhibitory effect of ethylene was reversible and could be relieved by Ag⁺. The Ag⁺-treated leaf discs, with or without ethylene, contained only free ACC at an increased level. The results suggest that in tobacco leaves, the autoinhibition of ethylene production resulted from reduction in the availability of free ACC, through both suppression of ACC formation and increased ACC conjugation.     

Catabolism of indole-3-acetic acid to indole-3-methanol in a crude enzyme extract and in protoplasts from Scots pine (Pinus sylvestris)

The antagonistic effects of ethylene and Ag⁺ on the metabolism of [1-¹⁴C]indole-3-acetic acid (IAA) and on the rates of ethylene production were studied in tobacco leaf discs ( Nicotiana rustica var. Brasilia ). During the first 10 h of incubation, Ag⁺-pretreated leaf discs contained more free [¹⁴C]IAA than untreated ones due to decreased oxidative decarboxylation, and the discs also produced more ethylene. Exogenously supplied ethylene nullified these effects of Ag⁺. However, the most pronounced effect of Ag⁺ in increasing ethylene production, as well as the strongest antagonistic effect of exogenous ethylene, were found between 24 and 48 h of incubation. During this time span no effect on the level of free IAA and on its decarboxylation could be observed. It is suggested that ethylene exerted its autoinhibitory effect by a feedback control on the IAA-induced ethylene biosynthesis. Possible mechanisms for the autoinhibitory effect of ethylene are discussed.